The present invention relates generally to beam balance instruments and is particularly concerned with a reinforced base assembly for balanced beam manometers as used in liquid depth gauging to measure pressure variations as a result of depth changes.
Beam balances are commonly used in weighing, and accurate microbalances can measure very small weight differences. The beam balance principle has also been used in measuring pressure, substituting the force of a pressurized bellows for the weight to tilt the beam, so that a measure of the amount of tilt provides an indication of the applied force. Pressure responsive beam balance instruments are commonly used with a so-called "bubbler system" for monitoring liquid levels in tanks, reservoirs, and the like. In such systems, a trace flow of pressurized gas is passed down a bubbler tube extending into the liquid to a location close to the bottom, and the resultant pressure is measured at a convenient location via a suitable pressure responsive instrument, such as a beam balance. In the balanced beam or manometer, the pressurized line is connected to a bellows, and the bellows force is in turn applied to the beam of the manometer to change its tilt in response to pressure changes. A sensor is arranged to detect the null position of the beam, and is connected to a suitable drive mechanism to drive a poise along the beam to counterbalance the force applied by the bellows and return the beam to the null position. The travel of the poise is therefore proportional to the applied pressure, which in turn will be dependent on the liquid depth.
Instruments of the balanced beam manometer type are described in my U.S. Pat. Nos. 4,266,430, 4,274,039 and 4,277,981. In my co-pending application Ser. No. 07/411,873 filed Sep. 25, 1989, a technique for compensating for gas weights and other errors in such instruments as well as in other types of pressure responsive, liquid depth gauging instruments is described.
However, even with these error compensations it was found that some ambient temperature drift still existed in the balance beam manometer instrument, as a result of "squirming" of the sheet metal chassis with temperature change when this economical means of manufacture was first employed.